In the prior art relating broadly to closure release devices, a solenoid-retained (or actuated) mechanism employing a toggle linkage is well known.
For example, in the U.S. Pat. No. 3,207,273, to Jurin, opening of the door causes it to engage a roller carried by a switch arm pivotably mounted on a fixed pin, and the switch arm pivots to close a switch to energize a solenoid. When the solenoid is energized, its armature is retracted, thereby lifting a link pivotably connecting the armature to the junction of a pair of toggle levers. The other end of one of the toggle levers is pivoted on a fixed pin, while the respective other end of the other lever is pivotably connected to a support lever. This support lever carries a brace pivotably mounted on the fixed pivot pin for the switch arm. Because of the toggle linkage, the support lever rotates clockwise (in the orientation shown). A catch arm subassembly is carried on the end of the support lever and is lowered into position on the other side of the door. A roller on the lowermost end of the catch arm subassembly engages the other side of the door and cooperates with the roller on the switch arm to retain the door in its open position. When the solenoid is de-energized, the toggle linkage falls (by gravity) into its alternate position; the support lever rotates counterclockwise; and the catch arm subassembly is lifted sufficiently to clear its roller and allow the door to be closed.
In a co-pending application for U.S. patent, Ser. No. 263,955, entitled "Emergency Exit Door Latch With Hydraulic and Electric Delay", now U.S. Pat. No. 4,470,625 issued on Sept. 11, 1984 assigned to the assignee of the present invention, a toggle linkage is connected to a latch by means of a hydraulic cylinder, and the solenoid is disposed between the latch and the toggle linkage. The hydraulic cylinder is designed to provide a hydraulic-type of time delay, which provides a fail-safe back-up system for an electronically-activated time delay for de-energizing the solenoid.
Moreover, in commercially-available magnetic door latches, energization of a solenoid is intended to attract a spring-loaded cylindrical bolt made of a magnetic material, thereby maintaining the door in a latched or locked position. De-energization of the solenoid, as by insertion of a magnetically-coded card, will release the spring-loaded bolt for opening the door and gaining access therethrough. These magnetic door latches, which are widely used for security purposes in governmental, industrial and commercial facilities, are relatively expensive. Their installation requires a precision "male/female" alignment between the bolt and the solenoid. The tolerances are critical, thereby escalating the cost. Moreover, any settlement of the building structure over time may cause misalignments between the bolt and its solenoid, thereby causing the conventional magnetic door latch to jam or otherwise malfunction. As a result, service calls are relatively frequent, and security or access is temporarily interrupted.
While this problem with respect to conventional magnetic door latches has persisted for many years, no one to date has conceived or developed a commercially-practical solution involving the use of a solenoid-retained toggle linkage for the purposes intended.